Placing information in the form of electrical signals, usually in the audio ranges, onto a much higher frequency signal for the purpose of transmitting that information through space is called modulation. Radio and television transmission at different assigned frequencies or narrow frequency bands, determined by the higher frequency signal (the carrier frequency), is detected at the receiving end by tuning the receiver to the desired frequency band. The signals then are "demodulated" to provide the audio signals or other electrical signals at the receiver. Typically, the signal which is being modulated (the carrier signal) is a sine wave signal of constant amplitude. The signal which then varies some parameter of this sine wave carrier signal (either its amplitude or phase, for example) is known as the modulating signal.
Amplitude modulation of a carrier signal is widely used; and the particular form has different subdivisions, such as double sideband (DSB), single sideband (SSB), variable sideband (VSB), and others. Circuits for providing these different types of modulation are common and well known. In simple amplitude modulation, typically there are two sidebands generated (DSB) and each of these sidebands contains approximately one-sixth (1/6th) of the total power. At the receiver, only one of the two sidebands is used to demodulate the signal. The energy or power in the other sideband is wasted.
Single sideband transmission without a carrier is a relatively efficient transmission technique, but it is complex and requires extensive circuits and phase and frequency matching to reinsert the carrier at the receiver prior to demodulation of the desired modulating signal. Single sideband transmission may be considered a simple frequency translation of the baseband (information) or modulating signal to a higher frequency more suitable for propagation from a transmitter to a receiver.
The known amplitude modulation systems, single sideband or double sideband, typically have a limit on the relative strength of the modulating signal to the strength of the carrier signal. This limit is considered 100% modulation, that is, the modulating signal cannot exceed the strength of the carrier signal. Typically, the power of the carrier signal is selected in accordance with the desired transmitting characteristics, and the modulating signal (which contains the desired information) is a relatively small fraction of the carrier signal.
Other types of signal modulation, such as phase or frequency modulation, also are widely employed. Phase and frequency modulation transmission enjoy advantages over amplitude modulation transmission, primarily in the relative freedom from static and other signal distortion which occurs in amplitude modulation transmission due to weather conditions and other factors. The basic underlying techniques for combining the carrier signal and the modulating signal (the desired information signal), however, are similar, regardless of which type of modulation is employed. The carrier signal is selected to be of a higher power than the modulating or information signal.
Typical transmitting stations, whether for AM transmission, FM transmission, or television transmission, operate at extremely high power levels. For such stations to have any reasonable range or receiving area, the transmitting power is many thousands of watts. Consequently, the transmitting station equipment is necessarily expensive because of the high power requirements of all of the components used to produce and transmit the radio frequency signals. In addition, because of the high levels of power consumption, the basic cost of the electricity used by such stations is very high and constitutes a significant percentage of the expense of operating the stations.
Typical transmitting stations combine the various signals together, prior to transmission, through the use of active amplifier and active electronic mixing devices. Multiple plate vacuum tubes and similar components are utilized for this purpose. Because of the high power requirements, the electronic components are large and expensive. The high power requirements also subject transmitting stations to relatively high maintenance requirements. Typically, maintenance engineers are actively on duty during at least a major portion of the transmitting day.
It is known that when alternating current flows through a conductive coil (any coil), the current first flows in one direction through the coil for one half-cycle of the driving alternating voltage and then flows in the opposite direction through the other half-cycle of the alternating driving voltage. The first half of the positive half-cycle is an acceleration voltage and the other half of the positive half-cycle is a deceleration voltage. The voltage starts at zero and then increases to a peak at the mid point of the first half-cycle and then decreases back to zero to complete such a half-cycle. The following opposite half-cycle is the same, except that the acceleration-peak-deceleration voltage is exactly reversed in direction from that of the preceeding half-cycle.
The charge carrier motion of this current generates a magnetic field, which is at right angles to the direction of the charge carrier motion in the wire of the coil. Consequently, the coil is surrounded by a magnetic flux with a north/south orientation at any given moment of time. This orientation is dependent upon the direction of the current in the coil.
Obviously, if the current in the coil is a direct current (DC), the coil has a permanent non-varying north/south orientation. This is the same as the magnetic flux or magnetic field around a flat circular ceramic magnet which has a hole in its center. Empirically, such a magnet is identical to a torodial coil energized by a DC current. The amount of current (power) necessary to cause a coil to have the same magnetic flux intensity (gauss intensity) as a given ceramic magnet intensity is very high. Consequently, the use of a ceramic magnet instead of a coil represents great savings in the amount of power necessary to produce the same magnetic effect.
Faraday's "lines of force", along with magnetic north poles and magnetic south poles, are created fictions for the sake of mathematical formulas dealing with magnetism and also to provide a way of producing mental pictures useful in studying magnetic theories. Such magnetic poles and lines of force are not actual facts of Physics or objective items. There are neither "lines of force" nor "magnetic poles". What does exist is a direction of the movement of charge carriers, electrons, etc. in a conductor under the influence of a driving force or voltage. In a coil, the direction of this movement determines if the top of the coil is a magnetic "north" pole or is a "south" pole, and the north/south orientation is at right angles to the direction of the charge carriers or electron flow in the wire or coil. Even a single electron in a circular orbit produces a magnetic dipole with a north/south orientation. This orientation is at right angles to the orbit of the electron as determined by the relative direction of the movement of the electron in such orbit.
It also is known that when two coils are placed in close proximity to one another, a change in the magnetic flux of one of these coils, either caused by a magnet being pushed or pulled into the coil, or caused by a change in the current flowing through the coil, causes a corresponding change in the flux of the other coil. Both coils are inductively coupled by the magnetic flux, and the coil which is connected only by the magnetic field or magnetic flux has an electromagnetic force induced in it by changes in the flux of the other or inducing coil. This induced electromagnetic force (EMF) is proportional to the rate at which the current is changing in the inducing coil. The induced current appears in such a direction that it opposes the change that produces it.
It is desirable to provide a modulation and/or frequency multiplier system which is not subject to the limitations of the known transmitting art, and which utilizes the unique characteristics of magnetic induction to provide simple, low cost generation of any desired modulation type.